This application is based on Patent Application Nos. 2001-024549 filed Jan. 31, 2001 in Japan and 2002-003917 filed Jan. 10, 2002 in Japan, the contents of which are incorporated hereinto by reference.
1. Field of the Invention
The present invention relates to a liquid ejection head, a suction recovering method, a head cartridge incorporating the liquid ejection head and an image forming apparatus using the liquid ejection head.
In this Specification, a word xe2x80x9cprintxe2x80x9d refers to not only forming a significant information, such as characters and figures, but also forming images, designs or patterns on a printing medium and processing such as etching and so forth in the printing medium, whether the information is significant or insignificant or whether it is visible so as to be perceived by humans.
The term xe2x80x9cprinting mediumxe2x80x9d includes not only paper used in common printing apparatus, but also sheet materials such as cloths, plastic films, metal sheets, glass plates, ceramic sheets, wood panels and leathers or three-dimensional materials such as spheres, round pipes and so forth which can receive the ink.
Further, the word xe2x80x9cinkxe2x80x9d should be interpreted in its wide sense as with the word xe2x80x9cprintxe2x80x9d, refers to liquid that is applied to the printing medium for forming images, designs or patterns, processing such as etching in the printing medium or processing such as coagulating or insolubilizing a colorant in the ink and includes any liquids used for printing.
2. Description of the Related Art
Ink jet printers may inappropriately eject a liquid, that is, ink and/or a treatment liquid that adjusts the printability of the ink on a printing medium, when the entire apparatus may not be used over a long period or the liquid is rarely ejected from particular ones of many ejection ports compared to the others. This is because the liquid evaporates in the ejection ports or liquid channels that are in communication therewith, thereby increasing the viscosity of the ink. Ejected droplets of the liquid or water or dusts may be accreted to an ejection surface of an ink jet head having the ejection ports disposed therein, and newly ejected liquid droplets may pulled by these depositions and thus ejected in a biased direction.
To prevent these inconveniences, conventional ink jet printers comprise the following means as what is called an ejection recovering device, e.g. preliminary ejecting means for ejecting the liquid to liquid receiving element before a print operation to remove viscosity-increased ink, liquid sucking means for sucking the liquid from the ejection ports or a common liquid chamber to remove the depositions, and capping means for preventing the liquid from evaporating through the ejection ports.
Ink jet printers which can print colored images have been developed which comprise one ink jet head having a group of ejection ports for black color as well as ejection port groups for color inks, for example, yellow, magenta, and cyan inks, an independent ink tank and an independent ink supply system provided for each group of ejection ports, and a common recovering cap and a common ejection recovering means shared by all the ejection port groups. Ink jet printers of this kind form color print images other than black ones using two or three colors. In this case, if the amount of color ink ejected per dot is equal to that of black ink ejected per dot, ink dots printed on the printing medium such as paper have an excessively large diameter. Thus, the ejection ports for the color inks have a smaller diameter than those for the black ink or the liquid channels that are in communication with the ejection ports for the color inks have a cross sectional area different from that of the liquid channels which are in communication with the ejection ports for the black ink. With what is called a bubble jet method of ejecting liquid droplets on the basis of heating by electrothermal transducers or the like, the electrothermal transducers for the color inks have a smaller area or the distance between the electrothermal transducers and ejection ports for the color inks is different from that for the black ink. With ink jet printers using plural types of inks having different shading, the same ink jet head or head cartridge has a plurality of ejection port groups formed therein, and the ejection ports of each ejection port group and the liquid channels that are in communication with the ejection ports have different diameters and cross sectional areas, respectively.
To improve the quality of print images and printing speed, ink jet heads have been designed which use the above described ink jet head technique for multicolor inks or inks with different colorant concentrations to eject common ink from a plurality of ejection port groups having different opening areas.
It is assumed that a suction recovering process is performed on a liquid ejection head comprising a liquid supplying port to which a liquid is supplied, liquid supplying passages having one end in communication with the liquid supplying port, a common liquid chamber that is in communication with the other end of each of the liquid supplying passages, and ejection port groups from which liquid droplets are ejected. In this case, when the liquid is simultaneously sucked through a ejection port group having a larger sum of opening areas of the ejection ports and from a ejection port group having a smaller sum of opening areas of the ejection ports, a larger amount of liquid tends to be sucked in the former case.
If the individual liquid channels that are in communication with the ejection port groups have substantially the same volume, substantially the same amount of liquid is discharged during suction recovery. Thus, when the suction recovering process is performed in favor of the ejection port group having a smaller sum of opening areas of the ejection ports, more than a required amount of liquid is sucked and ejected from the ejection port group having a larger sum of opening areas of the ejection ports. As a result, the liquid is wastefully consumed.
With ink jet heads using liquid tanks incorporating porous members such as sponge which holds the liquid, if different amounts of liquid are sucked and ejected from the respective tanks, then bubbles may be contained in the liquid supplying passages in an ink jet head having liquid tanks connected thereto and from which larger amounts of liquid are discharged.
It is an object of the present invention to provide a liquid ejection head wherein when a liquid is simultaneously sucked through a plurality of ejection port groups having different passage resistances, substantially the same amount of liquid is sucked through the individual ejection port groups or the amounts of liquid sucked through the individual ejection port groups are adjusted to be the same.
It is another object of the present invention to provide a liquid ejection head wherein when a liquid is simultaneously sucked through a plurality of ejection port groups having different ejection port configurations, the liquid can be efficiently sucked, and bubble are prevented from being taken in liquid channels, while restraining the liquid from being wastefully consumed.
It is yet another object of the present invention is to provide a suction recovering method wherein when a liquid is simultaneously sucked through a plurality of ejection port groups having different ejection port configurations, the liquid can be efficiently sucked, and bubble are prevented from being taken in liquid channels, while restraining the liquid from being wastefully consumed, as well as a head cartridge and an image forming apparatus both incorporating a liquid ejection head that can implement such a suction recovering method.
A first aspect of the present invention is in a liquid ejection head comprising a liquid supplying passage having one end in communication with a liquid supplying port to which a liquid is supplied, the liquid supplying passage branching into a plurality of branching paths by the way, a plurality of common liquid chambers which are in communication with the respective ones of the plurality of branching paths, and a plurality of opening groups which are in communication with the respective common liquid chambers via liquid channels and which are opened to the atmosphere, wherein a cross sectional area of the branching path which is in communication with one of the plurality of opening groups which has a larger sum of opening areas is smaller than a cross sectional area of the branching path which is in communication with the opening group which has a smaller sum of opening areas.
A second aspect of the present invention is in a liquid ejection head comprising a liquid supplying passage having one end in communication with a liquid supplying port to which a liquid is supplied, the liquid supplying passage branching into a plurality of branching paths by the way, a plurality of common liquid chambers which are in communication with the respective ones of the plurality of branching paths, and a plurality of opening groups which are in communication with the respective common liquid chambers via liquid channels and which are opened to the atmosphere, wherein a length of the branching path which is in communication with one of the plurality of opening groups which has a larger sum of opening areas is longer than a length of the branching path which is in communication with the opening group which has a smaller sum of opening areas.
A third aspect of the present invention is in a liquid ejection head comprising a liquid supplying passage having one end in communication with a liquid supplying port to which a liquid is supplied, the liquid supplying passage branching into a plurality of branching paths by the way, a plurality of common liquid chambers which are in communication with the respective ones of the plurality of branching paths, and a plurality of opening groups which are in communication with the respective common liquid chambers via liquid channels and which are opened to the atmosphere, wherein a branching portion of the branching path which is in communication with one of the plurality of opening groups which has a larger sum of opening areas is more downstream in a liquid flowing direction than a branching portion of the branching path which is in communication with the opening group which has a smaller sum of opening areas.
In the liquid ejection head according to the third aspect of the present invention, three or more opening groups may be provided.
According to the liquid ejection heads according to the first to third aspects of the present invention, the cross sectional area of the branching path which is in communication with one of the plurality of opening groups which has a larger sum of opening areas is smaller than the cross sectional area of the branching path which is in communication with the opening group which has a smaller sum of opening areas, or a length of the branching path which is in communication with one of the plurality of opening groups which has a larger sum of opening areas is longer than a length of the branching path which is in communication with the opening group which has a smaller sum of opening areas, or in particular three or more ejection port groups are provided, the branching portion of the branching path which is in communication with one of the plurality of opening groups which has a larger sum of opening areas is more downstream in a liquid flowing direction than a branching portion of the branching path which is in communication with the opening group which has a smaller sum of opening areas. Accordingly, the amount of liquid sucked through the ejection port group having a larger sum of opening areas of the ejection ports can be made substantially equal to the amount of liquid sucked through the ejection port group having a smaller sum of opening areas of the ejection ports, therefore restraining the wasteful discharge of the liquid associated with a suction recovering process.
A fourth aspect of the present invention is in a liquid ejection head comprising a liquid supplying passage having one end in communication with a liquid supplying port to which a liquid is supplied, the liquid supplying passage branching into a plurality of branching paths by the way, a plurality of common liquid chambers which are in communication with the respective ones of the plurality of branching paths, and a plurality of opening groups which are in communication with the respective common liquid chambers via liquid channels and which are opened to the atmosphere, wherein the plurality of opening groups include, an opening group that is composed of a plurality of ejection ports arranged at predetermined intervals to eject the liquid to a printing medium, and liquid discharging ports disposed adjacent to the ejection ports which are located at each end of the plurality of the ejection ports in an arrangement direction thereof, the liquid discharging ports not relating to formation of images on the printing medium, and an opening group which is composed only of the ejection ports.
A fifth aspect of the present invention is in a liquid ejection head comprising a plurality of opening groups which are in communication with the respective ones of a plurality of common liquid chambers via liquid channels and which are opened to the atmosphere, the plurality of opening groups each having a plurality of ejection ports arranged at predetermined intervals to eject the liquid to a printing medium, and liquid discharging ports disposed adjacent to the ejection ports which are located at each end of the plurality of the ejection ports in an arrangement direction thereof, the liquid discharging ports not relating to formation of images on the printing medium, wherein the number of the liquid discharging ports in one of the plurality of opening groups which has a larger sum of opening areas of the ejection ports are fewer than the number of the liquid discharging ports in the opening group which has a smaller sum of opening areas of the ejection ports.
A sixth aspect of the present invention is in a liquid ejection head comprising a plurality of opening groups which are in communication with the respective ones of a plurality of common liquid chambers via liquid channels and which are opened to the atmosphere, the plurality of opening groups each having a plurality of ejection ports arranged at predetermined intervals to eject the liquid to the printing medium and liquid discharging ports disposed adjacent to the ejection ports which are located at each end of the plurality of the ejection ports in an arrangement direction thereof, the liquid discharging ports not relating to formation of images on the printing medium, wherein the sum of opening areas of the liquid discharging ports in one of the plurality of opening groups which has a larger sum of opening areas of the ejection ports is smaller than the sum of opening areas of the liquid discharging ports in the opening group which has a smaller sum of opening areas of the ejection ports.
According to the liquid ejection heads according to the fourth to sixth aspects, the plurality of opening groups include an opening group that is composed of a plurality of ejection ports arranged at predetermined intervals to eject the liquid to a printing medium and liquid discharging ports disposed adjacent to the ejection ports which are located at each end of the plurality of the ejection ports in an arrangement direction thereof, the liquid discharging ports not relating to formation of images on the printing medium, and an opening group that is composed only of the ejection ports, or the number of the liquid discharging ports in one of the plurality of opening groups which has a larger sum of opening areas of the ejection ports are fewer than the number of the liquid discharging ports in the opening group which has a smaller sum of opening areas of the ejection ports, or the sum of opening areas of the liquid discharging ports in one of the plurality of opening groups which has a larger sum of opening areas of the ejection ports is smaller than the sum of opening areas of the liquid discharging ports in the opening group which has a smaller sum of opening areas of the ejection ports. Accordingly, the amount of liquid sucked through the ejection port group having a larger sum of opening areas of the ejection ports can be made substantially equal to the amount of liquid sucked through the ejection port group having a smaller sum of opening areas of the ejection ports, therefore the suction recovering process for the liquid ejection head can be effectively performed.
In the liquid ejection heads according to the first to sixth aspects of the present invention, at least one of the plurality of opening groups has a different number of openings from those of the other opening groups. Alternatively, at least one of the plurality of opening groups has at least one opening, the area of which is different from those of the openings of the other opening groups.
When at least one of the plurality of opening groups has a different number of openings from those of the other opening groups, particular liquid droplets can be printed at a higher speed than the other liquid droplets. For example, when the opening group for black ink has more openings than the opening groups for cyan, magenta, and yellow inks, the production costs of a print head can be reduced, and the monochromatic printing speed can be increased.
When at least one of the plurality of opening groups has at least one opening, the area of which is different from those of the openings of the other opening groups, then by forming smaller- and larger-droplet ejection ports for each of the ejection port groups for the cyan and magenta inks, while forming only larger-droplet ejection ports for the ejection port group for the yellow ink, which involves unnoticeable ink droplets, the production costs of the print head can be reduced, and different amounts of ink droplets can be ejected from each of the ejection port groups for the cyan and magenta inks. Thus, the printing speed and image quality can be improved by appropriately selecting ejected dots, for example, ejecting larger ink droplets for high-duty images with unnoticeable dots, while ejecting smaller ink droplets for low-duty images with noticeable dots.
In the liquid ejection heads according to the fifth and sixth aspects of the present invention, the plurality of common liquid chambers may be in communication with the respective ones of a plurality of branching paths of a liquid supplying passage having one end in communication with the liquid supplying port to which the liquid is supplied, the liquid supplying passage branching into the plurality of branching paths by the way.
The seventh aspect of the present invention is in a liquid ejection head comprising a plurality of head portions each having a liquid supplying passage having one end in communication with a liquid supplying port to which a liquid is supplied, the liquid supplying passage branching into a plurality of branching paths by the way, a plurality of common liquid chambers which are in communication with the respective ones of the plurality of branching paths, and a plurality of opening groups which are in communication with the respective common liquid chambers via liquid channels and which are opened to the atmosphere, at least one of all the opening groups having a different number of openings from those of the other opening groups, wherein the sum of the opening areas in one of all the opening groups which has the largest sum is 1.6 or less times the sum of the opening areas in the other opening group which has the smallest sum, and wherein the sum of the areas of the openings constituting the plurality of opening groups in one of the plurality of head portions which has the largest sum is 5 or less times the sum of the areas of the openings constituting the plurality of opening groups in the other head portion which has the smallest sum.
The eighth aspect of the present invention is in a liquid ejection head comprising;
a first head portion having a liquid supplying passage having one end in communication with a liquid supplying port to which a liquid is supplied, the liquid supplying passage branching into a plurality of branching paths by the way, a plurality of common liquid chambers that are in communication with the respective ones of the plurality of branching paths, and a plurality of opening groups which are in communication with the respective common liquid chambers via liquid channels and which are opened to the atmosphere, and
a second head portion having common liquid chambers that are in communication with a liquid supplying port to which a liquid is supplied, and opening groups which are in communication with the respective common liquid chambers via liquid channels and which are opened to the atmosphere,
at least one of all the opening groups having a different number of openings from those of the other opening groups,
wherein the sum of the opening areas in one of all the opening groups which has the largest sum is 1.6 or less times the sum of the opening areas in the other opening group which has the smallest sum, and
wherein the sum of the areas of the openings constituting the plurality of opening groups in one of the first and second head portions which has the largest sum is 5 or less times the sum of the areas of the openings constituting the plurality of opening groups in the other head portion which has the smallest sum.
The ninth aspect of the present invention is in a liquid ejection head comprising a plurality of head portions each having a liquid supplying passage having one end in communication with a liquid supplying port to which a liquid is supplied, the liquid supplying passage branching into a plurality of branching paths by the way, a plurality of common liquid chambers which are in communication with the respective ones of the plurality of branching paths, and a plurality of opening groups which are in communication with the respective common liquid chambers via liquid channels and which are opened to the atmosphere, at least one of all the opening groups having at least one opening, the area of which is different from those of the openings of the other opening groups, wherein the sum of the opening areas in one of all the opening groups which has the largest sum is 1.6 or less times the sum of the opening areas in the opening group which has the smallest sum, and wherein the sum of the areas of the openings constituting the plurality of opening groups in one of the plurality of head portions which has the largest sum is 5 or less times the sum of the areas of the openings constituting the plurality of opening groups in the other head portion which has the smallest sum.
The tenth aspect of the present invention is in a liquid ejection head comprising;
a first head portion having a liquid supplying passage having one end in communication with a liquid supplying port to which a liquid is supplied, the liquid supplying passage branching into a plurality of branching paths by the way, a plurality of common liquid chambers that are in communication with the respective ones of the plurality of branching paths, and a plurality of opening groups which are in communication with the respective common liquid chambers via liquid channels and which are opened to the atmosphere, and
a second head portion having common liquid chambers which are in communication with a liquid supplying port to which a liquid is supplied, and opening groups which are in communication with the respective common liquid chambers via liquid channels and which are opened to the atmosphere,
at least one of all the opening groups having at least one opening, the area of which is different from those of the openings of the other opening groups,
wherein the sum of the opening areas in one of all the opening groups which has the largest sum is 1.6 or less times the sum of the opening areas in the other opening group which has the smallest sum, and
wherein the sum of the areas of the openings constituting the plurality of opening groups in one of the first and second head portions which has the largest sum is 5 or less times the sum of the areas of the openings constituting the plurality of opening groups in the other head portion which has the smallest sum.
According to the liquid ejection heads according to the seventh to tenth aspects of the present invention, the sum of the opening areas in one of all the opening groups which has the largest sum is 1.6 or less times the sum of the opening areas in the other one of all the opening groups which has the smallest sum, and the sum of the areas of the openings constituting the plurality of opening groups in one of the first and second head portions which has the largest sum is 5 or less times the sum of the areas of the openings constituting the plurality of opening groups in the other head portion which has the smallest sum. Accordingly, the amount of liquid sucked from the head section having the largest sum of opening areas of the ejection ports can be made substantially equal to the amount of liquid sucked from the head section having the smallest sum of opening areas of the ejection ports, therefore restraining the wasteful discharge of the liquid associated with a suction recovering process.
In the liquid ejection heads according to the first to third and seventh to tenth aspects of the present invention, the opening group may have a plurality of ejection ports arranged at predetermined intervals to eject the liquid to a printing medium, and liquid discharging ports not relating to formation of images on the printing medium and disposed adjacent to those of the ejection ports which are located at each end of the plurality of ejection ports in an arrangement direction thereof. In this case, bubbles that may be collected at the opposite ends of the common liquid chamber can be effectively removed through the liquid discharging port during suction recovery.
In the liquid ejection heads according to the first to tenth aspects of the present invention, the opening groups may be covered by a common capping member before a sucking operation is performed. In this case, the suction recovering process for the liquid ejection head can be effectively performed.
In the liquid tank in which the liquid is stored and which have the porous members for retaining the liquid, when a large amount of liquid is sucked during suction recovery, air passages may be formed in the porous members to draw bubbles into the liquid channels of the liquid ejection head, thereby degrading images. However, the liquid ejection head of the present invention can achieve a good suction recovering process.
Each of the liquid channels may be provided with an ejection energy generating portion that causes liquid droplets to be ejected from the openings. In this case, the ejection energy generating portion may have an electrothermal transducer that generates thermal energy required to cause film boiling in the liquid.
In the liquid ejection heads according to the seventh to tenth aspects of the present invention, the sum of the opening areas in the opening group having the largest sum may be substantially equal to the sum of the opening areas in the opening group having the smallest sum. In this case, the amounts of liquid sucked through these opening groups can be made substantially equal.
In the liquid ejection heads according to the ninth and tenth aspects of the present invention, at least one of all the opening groups may have a different number of openings from those of the other opening groups. In this case, particular liquid droplets can be printed at a higher speed than the other liquid droplets. For example, when the opening group for black ink has more openings than the opening groups for cyan, magenta, and yellow inks, the production costs of a print head can be reduced, and the monochromatic printing speed can be increased.
The eleventh aspect of the present invention is in a suction recovering method of simultaneously sucking a liquid through all opening groups of a liquid ejection head according to any one of the first to tenth aspects of the present invention to allow liquid droplets to be appropriately ejected from the opening groups, the amounts of liquid sucked through the opening groups are substantially equal. According to the present invention, in simultaneously sucking the liquid through the plurality of ejection port groups of the liquid ejection head to allow liquid droplets to be always appropriately ejected from the plurality of ejection port groups, the amounts of liquid sucked through the ejection port groups are made substantially equal. This restrains the wasteful discharge of the liquid associated with a suction recovering process, therefore achieving an efficient suction recovering process.
A twelfth aspect of the present invention is in a head cartridge comprising a liquid ejection head according to any one of the first to tenth aspects of the invention, and a liquid tank storing a liquid supplied to the liquid ejection head via a liquid supplying port provided to the liquid ejection head.
In the head cartridge according to the twelfth aspect of the present invention, the liquid tank may be detachably attached to the liquid ejection head.
A thirteenth aspect of the present invention is in an image forming apparatus for forming an image on a print medium by using a liquid ejected from a plurality of ejection port groups of a liquid ejection head according to any one of the first to tenth aspects of the present invention or from a plurality of ejection port groups of a liquid ejection head of a head cartridge according to the twelfth aspect of the present invention, the apparatus comprising a mounting portion for mounting the liquid ejection head or the head cartridge, means for feeding the printing medium, a capping member that can cover a ejection port surface in which the plurality of ejection port groups of the liquid ejection head are opened, and suction recovering means for sucking a liquid present in the liquid ejection head, through the plurality of ejection port groups via the capping member.
In the image forming apparatus according to the thirteenth aspect of the present invention, the mounting portion may have a carriage for scanning in a direction crossing a direction in which the printing medium are fed. In this case, the liquid ejection head may be mounted so as to be detachably attached to the carriage via detaching means.
The liquid may be ink and/or a treatment liquid that adjusts printability of the ink on the printing medium.
The above and other objects, effects, features and advantages of the present invention will become more apparent from the following description of embodiments thereof taken in conjunction with the accompanying drawings.